As described in German patent document No. 3,137,774 filed 23 Sept. 1981 by W. P. Herring and in German patent document No. 3,510,835 filed 26 Mar. 1985 by J. Humpert and M. Pawelzic, a single-control mixing valve has a valve plate formed with hot-and cold-water inlet ports and a mixed-water outlet port, and a control plate slidable on this valve plate and formed with a mixing cavity that can be aligned with the ports to allow flow from the inlet ports to the outlet port. The valve plate can be moved back and forth to vary the volume of flow from the inlet ports and from side to side to vary the temperature of the water at the outlet port.
The valve and control plates are normally incorporated in a valve cartridge that is a replaceable part of a valve assembly that has a housing that covers the plates, a base plate that underlies the valve plate and that is formed with passages that connect downward to incoming and outgoing water lines and that mate upward with the ports in the valve plate, and a pivot assembly that in turn carries the operating lever. For replacement of the cartridge, the housing and lever are lifted off, the old cartridge is removed, the new cartridge is fitted in place, and the housing and lever are remounted over the new cartridge.
The housing is typically dimensioned with an eye toward style and economic construction while the cartridge is a standardized unit that does not vary over a wide range of different single-lever faucets. This creates a problem of fitting the various valve housings with the standard cartridge, something substantially complicated by the different diameters and heights of these housings.